Nuclear dependence of dimuon production at 800 GeV

A precise measurement of the atomic-mass dependence of dimuon production induced by 800-GeV protons is reported. Over 450 000 muon pairs with dimuon mass M{≥}4 GeV were recorded from targets of ²H, C, Ca, Fe, and W. The ratio of dimuon yield per nucleon for nuclei versus ²H, R=YA/Y2H, is sensitive to modifications of the antiquark sea in nuclei. No nuclear dependence of this ratio is observed over the range of target-quark momentum fraction 0.1xₜ0.3. For xₜ0.1 the ratio is slightly less than unity for the heavy nuclei. These results are compared with predictions of models of the European Muon Collaboration effect.